1. Field of the Invention
The present invention relates to a dry etching apparatus, and more specifically, to a dry etching apparatus capable of effectively exhausting reaction products in an etching chamber by adjusting vacuum conductance therein. The adjustment of vacuum conductance may be made possible by providing the dry etching apparatus with upper and lower electrodes having insulating rings with grooves therein. In addition, the adjustment of vacuum conductance may be made possible by providing the chamber of the dry etching apparatus with grooved sidewalls.
2. Background of the Related Art
In dry etching, an etching gas is supplied to and reacts with a material to be processed (e.g., a film on a wafer) to form products having high vapor pressure or high volatility. Accordingly, the etching gas is selected based on the consideration that desirable products be obtained by a reaction between the material and the etching gas. Since the material is generally formed of a silicon compound such as Si, SiO.sub.2, Si.sub.3 N.sub.4, and the like, an etching gas including a halogen element as a base (e.g., a fluorine based gas) is generally used for etching the silicon compound.
The dry etching is conventionally accomplished in an apparatus as schematically shown in FIG. 1. referring to the drawing, the structure of the dry etching apparatus will be described in detail hereinafter.
The dry etching apparatus includes a chamber 8 that provides a space for dry etching processes. A wafer 30 to be etched is transferred into the chamber 8. At the top of the chamber 8, a first gas duct 12 is formed to allow gas insertion from a gas supply 10. A vacuum pump 18 for providing vacuum pressure to the chamber 8 is connected to Ache bottom of the chamber 8 by a second gas duct 16, which opens into the chamber 8 at exhaust orifice 17. An upper electrode 13 and a lower electrode 14 are installed in the chamber 8 and maintain the pressure in the area where a discharge occurs.
Upper and lower electrodes 13 and 14 have a circular shape. The upper electrode 13 is spaced apart from and opposed to the lower electrode 14. FIGS. 2 and 4 show top views of the electrodes 13 and 14, respectively.
Referring to FIG. 2, the upper electrode 13 includes a gas diffuser plate 22 having a plurality of gas diffusers 24, and an insulation plate 20 fixed and installed around the gas diffuser plate 22 by a plurality of screws 15. The plurality of the screws 15 is arranged and installed in such a manner that the lines established by joining the center of the insulation plate 20 and two adjacent screws of the plurality of screws 15 form an angle of 45.degree., that is, the screws 15 are circumferentially spaced at 45.degree. intervals. The screws 15 are installed at a common radial distance from the center of the insulation plate 20.
FIG. 3 is a side view of the upper electrode 13 showing an incline area, having a predetermined width I, formed between the gas diffuser plate 22 and the insulation plate 20. The incline area is formed at an angle of 45.degree. with respect to the horizontal surface of the gas diffuser plate 22 or the insulation plate 20.
During the etching process, the gas diffuser plate 22 suitably mixes and uniformly distributes the etching gas supplied from the gas supply 10. When the mixed etching gas is uniformly distributed, the gas diffuser plate 22 spreads the mixed etching gas in a wide area.
The lower electrode 14, as shown in the top view of FIG. 4, includes a wafer stage 26 for supporting the wafer and an insulation plate 28 fixed and installed around the wafer stage 26 by a plurality of screws 15. The plurality of screws 15 are arranged and installed in the same manner as screws 15 in upper electrode 13, that is, they are circumferentially spaced at 45.degree. intervals.
As shown in FIG. 4, the outer edge of the wafer 30 and the outer edge of the wafer stage 26 define an exposed area having a width II on the wafer stage 26 when the wafer is placed thereon. In this embodiment, the wafer 30 is smaller than the wafer stage 26, however the wafer 30 may be the same size as the wafer stage 26.
P1, P2 and P3 in FIG. 1 are a front pressure of the gas diffuser plate 22, a back pressure of the gas diffuser plate 22 and a pressure of the exhaust orifice 17, respectively. P2 is actually the reaction pressure and, therefore, it is maintained at a predetermined level during the etching process.
The dry etching process in the dry etching apparatus begins with loading a wafer, ti which a material (e.g., an oxidation layer) to be etched is deposited, on the lower electrode 14 in the chamber 8. Under this condition, a gas, such as CF.sub.4, CHF.sub.3, He, Cl.sub.2, Ar, HBr, O.sub.2 and the like, is supplied to the chamber 8 from the gas supply 10. The material reacts with the gas and forms products having high vapor pressure or high volatility. As a result, the material is etched.
For example, assuming that a gas of 100 sccm is introduced into the chamber 8 from the gas supply 10 and the process pressure P2 is 2 Torr, the exhaust velocity S in the chamber 8 is calculated by the following formula, where Q is the quantity of the gas supplied to the chamber 8: ##EQU1##
Most reaction products (e.g., CO, HF and so on) have a low vapor pressure. Accordingly, the reaction products are converted into the gaseous state upon reacting with the material, and are exhausted through the exhaust orifice 17 and second gas duct 16 out of the chamber 8 at the exhaust velocity. However, the reaction products cannot be completely exhausted out of the chamber 8 due to the circumference temperature, pressure and other influences. As a result, some products (e.g., CnFn) remain and are accumulated to form a deposit, i.e., a polymer contaminant.
The polymer is a main source of contaminating particles during the etching process and induces an arc (also known as an insulation break), which adversely influences the Etching process.
The arc causes two main problems. First, in the event the temperature in the Chamber 8 exceeds a critical temperature (e.g., 130.degree. C.), a mask of a photoresist material is a transformed and cannot serve as a normal mask. This results in deteriorated patterns. Second, in the event a part of the gas diffuser plate 22 of the upper electrode 13 is broken away by an arc discharge, the broken part serves as contaminating particles in the etching process. This results in a defective etching process.
The polymer consists of various materials and is concentrated and accumulated mainly on the sidewalls of the chamber 8, around the exhaust orifice 17 of the second gas duct 16 and the area II on the lower electrode 14.
Accordingly, to suppress particle formation, the reaction products induced during the etching process should be guided in a predetermined direction and rapidly exhausted by enhancing the conductance of the exhaust orifice.